Service & test modes: Air Conditioner tips

Short, practical technician tips on service & test modes for air conditioner. Check each one against the manual for your exact model before acting.

Recall the active status code on the outdoor board (25VNA8/24VNA9)

Carrier · Carrier Infinity 25VNA8/24VNA9

Replays the most recent, highest-priority active status code on the amber STATUS LED; codes are kept without power. The unit does not heat or cool while the forced defrost pins are shorted.

1. Turn the unit power OFF
2. Short the FORCED DEFROST connector (J2 on the board) with a clip wire
3. Turn power ON; the amber LED flashes the stored code (short flashes = first digit, long flashes = second digit)
4. Power down and remove the short

Simulate a refrigerant leak with the RDS Test button

Lennox · Lennox EL16KC1 A/C with RDS blower control board 27A02 (R-454B)

After the 5-minute purge, pressing Test during a call makes the board act as if a leak was found, which checks wiring and response.

1. Restore power and wait for the 5-minute purge to finish.
2. Cooling check: start a cooling call at the thermostat, press Test on the RDS board, and confirm the LED flashes blue, the blower runs and the outdoor compressor stops.
3. Press Test again to end the simulated leak.
4. Heating check (gas furnace): start a heat call, press Test, and confirm the blue flashing LED, blower on, burners off and compressor off. Press Test again to end it.